Eratosthenes: Morocco measures the Earth

More than 2,200 years ago, the Greek astronomer Eratosthenes measured the Earth's circumference by comparing the shadow of two sticks planted in two different cities, at the same time. No satellites, no computers — just observation, a bit of geometry, and curiosity.

On September 23, 2026, Touriver Lab reproduces this experience at the scale of Morocco. Participants in several cities will each measure the angle of a shadow at the exact same moment. By comparing results through a dedicated app, we can recalculate the size of our planet — collectively.

This is the project officially launching the Touriver Lab program: participatory science, under the open sky, where you observe here to understand together.